Rotor blades, e.g. helicopter rotors, rotor blades of wind turbines and the like, are subject to erosion caused by the impact of airborne material, such as rain, sand, and dust. Of all parts of the rotor blades their leading edges are in particular prone to damage by erosion. The industry has sought means of protection against such erosion. For example, protective tapes or films may be applied to the leading edges of rotor blades. However, the application of tapes or films on rotor blades cannot be easily automated and is usually done by hand. This process can be time-consuming, in particular for applying films to rotor blades of great dimensions, as may be the case for rotor blades in wind turbines, in particular wind turbines for off-shore power stations. Such rotor blades may have a length of greater than 30 m or even greater than 60 m. Even rotor blades with a length of more than 100 m are currently contemplated.
Moreover, films have comparatively distinct edges which may negatively impact on the aerodynamic properties of the rotor blades.
Therefore, alternatives to protective films have been proposed.
An approach has been described, for example, in WO2010/122157 where a specific polyurethane protective coating based on polyesterpolyols is applied as the outermost layer on the rotor blade. The exemplified compositions provided in WO2010/122157 have been shown to be effective in a rain erosion test but contain considerable amounts of solvents (between 19 and 31% by weight), which is disadvantageous from an environmental point of view.
It has now been found that polyurethane based coatings of specific polyols and isocyanates can provide good protection against erosion, in particular rain erosion.